1. Field of the Invention
This invention relates to a semiconductor device such as a MOS transistor or the like and a method of manufacturing it, and particularly to a compact semiconductor device and a method of manufacturing it.
2. Description of the Related Art
In a MOS transistor, a drain current that flows between a source and a drain thereof formed in a semiconductor substrate, is controlled according to the value of a gate voltage corresponding to a voltage applied to a gate formed in relation to the source and drain thereof.
A threshold voltage of the gate, which allows the drain current, varies according to a potential applied to the semiconductor substrate. Thus, in order to control the potential of the semiconductor substrate, an electrode drawing or withdrawal portion used for an element or device region is formed in the device region for the MOS transistor, in which the source and drain are formed. A substrate electrode is provided at the electrode withdrawal portion independent of respective electrodes for the source and drain.
In order to obtain an ohmic contact between the substrate electrode and a device region for the semiconductor substrate, the electrode withdrawal portion is supplied with an impurity concentration higher than that of the device region by an impurity of the same conduction type as in the device region.
When the MOS transistor is now used as a digital circuit component such as an inverter or the like, it is necessary to maintain the potential of the semiconductor substrate, i.e., a potential applied to a well when the MOS transistor is formed in the well corresponding to the device region for the semiconductor substrate, for example, at a predetermined value.
Therefore, the substrate electrode provided at the electrode withdrawal portion for the device region is electrically connected to either one of the source and drain electrodes by an external interconnection to hold the substrate electrode at the same potential as that applied to the source or drain electrode.